In known techniques, an optical device, constituted by a hermetic sealing package including a hermetically sealed optical element, is used to suppress the effects of, for example, humidity on the optical element.
For example, Patent Literature 1 discloses a configuration in which an optical element is contained in a ceramic package, and the ceramic package is sealed by use of a metal cover after the ceramic package has been filled with inert gas. The cover has an opening in a central portion thereof, and the opening is sealed by a plate-shaped transparent window made from sapphire. The transparent window is bonded, on either the top or the bottom of the cover, to a portion of the cover along the opening.
Patent Literature 2 discloses an optical window package in which plate-shaped optical glass is provided on an upper side of a package so as to seal the interior of the package, a metal sealing being between the package and the optical glass. The optical glass has an opening in a central portion thereof, and this opening is formed by a pattern of metal deposited to a back side of the optical glass in a region excluding a region of the opening. With this configuration, the optical glass functions as a cover of the package.